This is not your father's Pong
Dave Quintana thought we might be interested in his latest experiment. He used Quartz Composer to create a Pong game (QCPong), which may very well be the first game written in Quartz Composer.
QCPong is a proof of concept game, so don't expect miracles. And Dave coded it so that the computer always wins, so it might drive you completely insane. But if Pong isn't your cup of tea, you'll be pleased to know that Dave is already working on QCBreakout.
Keep us posted, Dave!